Some facts about mercury, or another way to apply potassium permanganate

Mer­cury has been known to hu­man­i­ty from an­cient times. Al­chemists who strove to dis­cov­er the philoso­pher’s stone be­lieved that liq­uid mer­cury was the main com­po­nent of all met­als, and could turn into gold.

Mer­cury is the 80th el­e­ment in the pe­ri­od­ic ta­ble, and in na­ture this sub­stance is quite rare, but it is im­pos­si­ble to imag­ine mod­ern life with­out it. Mer­cury is ac­tive­ly used in met­al­lur­gy, and in chem­istry it is used to make amal­gams of met­als and con­duct var­i­ous ex­per­i­ments. It also plays a vi­tal role in medicine: re­mem­ber the or­di­nary ther­mome­ter, which con­tains mer­cury.

Ob­tain­ing mer­cury

In in­dus­try, mer­cury is ob­tained by the same method that was used in the past, which in­volves the fir­ing of cinnabar, i.e. bi­va­lent mer­cury sul­fide HgS, a red­dish-brown min­er­al. Dur­ing fir­ing, mer­cury va­por ac­cu­mu­lates, which is then col­lect­ed.

HgS + O₂ ⟶ Hg + SO₂↑

There is also a met­al­lother­mic method of ob­tain­ing mer­cury:

HgS + Fe ⟶ FeS↓ + Hg

Phys­i­cal prop­er­ties of mer­cury

Mer­cury is the only chem­i­cal el­e­ment of its kind which is a liq­uid met­al of a whitish-sil­very col­or un­der stan­dard con­di­tions. Hg melts at a tem­per­a­ture of -38.83 de­grees Cel­sius, and starts to boil at 356.73 °C.

With met­als, mer­cury may form al­loys – amal­gams. But it does not form amal­gams with some met­als, in­clud­ing iron. For this rea­son, mer­cury can be trans­port­ed in steel con­tain­ers.

Mer­cury dis­plays a rel­a­tive­ly low chem­i­cal ac­tiv­i­ty. The only thing that can dis­solve this met­al is aqua re­gia, a mix­ture of con­cen­trat­ed acids, hy­drochlo­ric and ni­tric, and also ni­tric acid (di­lut­ed or con­cen­trat­ed) and sul­fu­ric acid. The met­al is also quite sta­ble in air and does not mix with wa­ter.

Hg + 4H­NO₃ (con­cen­trat­ed) ⟶ Hg(NO₃)₂ + 2NO₂ + 2H₂O,

6Hg + 8H­NO₃ (di­lut­ed.) ⟶ 3Hg₂(NO₃)₂ + 2NO + 4H₂O,

Hg + 2H₂­SO₄ ⟶ Hg­SO₄ + SO₂ + 2H₂O.

Chem­i­cal prop­er­ties of mer­cury

Mer­cury also in­ter­acts with non-met­als: for ex­am­ple, at a tem­per­a­ture of over 300 de­grees Cel­sius, it re­acts with oxy­gen with the for­ma­tion of mer­cury(II) ox­ide:

2Hg + O₂ ⟶ 2HgO.

On heat­ing, mer­cury ac­tive­ly re­acts with sul­fur, and as a re­sult of the chem­i­cal re­ac­tion mer­cury (II) sul­fide forms.

Hg + S ⟶ HgS.

Mer­cury can en­ter into a re­ac­tion with halo­gens, for ex­am­ple with the green­ish-yel­low gas chlo­rine:

Hg + Cl₂ ⟶ Hg­Cl₂.

In­ter­ac­tion with acids

In the elec­tro­chem­i­cal se­ries, mer­cury comes af­ter hy­dro­gen: it does not in­ter­act with wa­ter, al­ka­lis or non-ox­i­diz­ing acids.

Tox­i­col­o­gy of mer­cury

Ev­ery­one re­mem­bers that it’s very dan­ger­ous to break a ther­mome­ter con­tain­ing mer­cury. Even school text­books tell you what to do in this sit­u­a­tion. In­deed, even in small amounts the sil­very-white met­al can be harm­ful to hu­man health.

But mer­cury can be neu­tral­ized with potas­si­um per­man­ganate, or as it is pop­u­lar­ly known, man­ganese crys­tals – pur­ple-black crys­tals which dis­solve well in wa­ter.

Here you’ll find easy and en­ter­tain­ing ex­per­i­ments with KM­nO₄.

Re­moval of mer­cury is called de­mer­cu­ra­tion, and potas­si­um per­man­ganate is used in tan­dem with oth­er sub­stances, for ex­am­ple, the “af­fect­ed area” is rinsed with a so­lu­tion of man­ganese crys­tals, and then with io­dine.